The broad concept of tiltably mounting wheels which are carried on opposite sides of a three-wheeled vehicle is not new and is disclosed, for example, in U.S. Pat. Nos. 3,480,098, 4,088,199 and 4,126,322. As used herein, the term `three-wheeled vehicle` includes a vehicle having two coaxial, transversely spaced apart wheels making two distinct points of engagement with the ground and a third wheel assembly longitudinally spaced from the latter two wheels and providing in effect a single-point engagement with the ground, even though this third wheel assembly may have plural closely spaced, coaxial wheels.
U.S. Pat. No. '098 discloses a three-wheeled tractor having a single front wheel steering assembly, two transversely spaced-apart rear drive wheels and an actuator-controlled levelling system for the latter which effects levelling of the tractor body about its longitudinal axis when the tractor operates on laterally inclined terrain, i.e. terrain which is inclined at an angle other than a straight angle relative to a normally horizontal ground plane.
U.S. Pat. No. '199 discloses a motorcycle-type vehicle having a single power-driven rear wheel assembly, two transversely spaced apart front steering wheels and a parallelogram-type balancing suspension linkage connected between the frame and the front wheels for allowing tilting movement between those wheels and the frame while the vehicle travels along or is parked on a laterally sloping incline or while the vehicle negotiates a turn at substantial forward speed. The tilting movement allows the frame and hence the body connected to the frame to remain substantially upright as the vehicle travels along a hillside, and it also allows the frame and hence the body to tilt relative to a horizontal plane, i.e. the ground, when the vehicle negotiates a turn; in both modes of operation, the wheels and the longitudinal vertical plane of the vehicle body remain parallel. No actuator for the suspension system is provided; tilting movement is effected by shifting of the operator's body.
U.S. Pat. No. '322 discloses a three-wheeled vehicle having a single power-driven rear wheel assembly, which is also used to steer the vehicle, and two transversely spaced apart front wheels which are connected to a vehicle frame by a parallelogram-type balancing suspension linkage providing tilting movement similar to that described above with respect to U.S. Pat. No. '199, except that in U.S. Pat. No. '322 control of the balancing system is effected by an actuator.
The broad concept of a three-wheeled vehicle having a driven single front wheel assembly is also known. For example, U.S. Pat. Nos. 2,503,106, 2,767,800 and 2,771,145 disclose such vehicles in which the front wheel is mechanically driven by an internal combustion engine, and U.S. Pat. No. 2,820,524 discloses such a vehicle in which the power source for the front wheel is a hydraulic motor.